1. Field of the Invention
The present invention is in the field of applied spectroscopy and, more particularly, in the field of integrated circuit inspection systems.
2. Description of Related Art
It is well known that in integrated circuit (IC) operation, current conduction through a damaged dielectric can cause it to emit extremely faint light. These photoemissions can be detected by the emission microscope disclosed in U.S. Pat. No. 4,680,635 to Khurana, as follows:
1. An IC or other such device ("device") to be tested is placed on a stage of a microscope having a camera associated therewith. A light-tight chamber is closed around the microscope.
2. The device is illuminated and repositioned if necessary within the system so that a particular part of the device to be inspected is positioned in the optic axis of the microscope and camera. Repositioning is effected by an operator viewing the device with a CRT display. The operator is capable of adjusting the Z axis elevation of the microscope stage to improve focus.
3. Next, without applying power, the illuminated device is imaged through a video camera to obtain a "reflected" light top view image of the structural pattern of the device. The reflected image is converted into digital form and stored. Storage is generally effected in a memory. Illumination may be either bright or dark field.
4. The illumination is turned off, and without applying power, any background noise light from the area to be inspected is collected and amplified in the video camera, and optionally in a digital image computer, to obtain a "background" image, which is digitized and stored.
5. Assuming that a defect in the device has previously been detected by some manner of automatic test equipment, a failure condition "test vector" of voltages is applied by manual switches to the I/O terminals of the device, still unilluminated, causing leakage current conducted through defective dielectric features to emit extremely faint visible and infrared light. This emitted light is collected and amplified to obtain an "emitted" light image, which is digitized and stored.
6. The digitized background image is subtracted from the digitized emitted image to produce a "difference" image showing defect emission bright spots, with some noise interference remaining.
7. The difference image is filtered or processed by an image processing computer to further separate emitted light points from the random noise bright points inherent to the very large signal amplification done in the primary camera. This processing is conventionally done on the basis of light intensity, e.g., gray level, threshold discrimination. This filtering produces a "processed difference" image.
8. The "processed difference" image is superimposed over the reflected image of the same area so that photon emission spots can be seen and located with respect to the device. With this information, a process or failure analysis engineer can, afterwards, refer to the composite layout of the device, determine the probably cause of failure, and correct the device design.
Various improvements have been made to emission microscopes such as that disclosed in U.S. Pat. No. 4,680,635. Certain of these improvements are discussed in, e.g., U.S. Pat. Nos. 4,755,874 and 4,811,090. Notwithstanding that improvements have been made, state of the art emission microscopes have a number of shortcomings and deficiencies. Several of these shortcomings and deficiencies relate to the data acquisition process. Succinctly stated, state of the art emission microscope systems lack an intelligently automated data acquisition subsystem.